Conventionally, a joining structure formed as a tabular reinforcing member or a U- or V-shaped reinforcing member, may be welded between a first columnar steel structural member and second structural member (such as a first columnar structural member crossing a tabular structural member or second columnar structural member—for example, see Japanese Patent Publication Nos. 2001-132102 and 2003-001476, the entire disclosures of which are incorporated herein by reference).
FIG. 8 shows a conventional joining structure in which tabular reinforcing members 12 are joined by welding between these structures a first columnar steel structural member 10 and a second structural member 11, and the bending moment of the second structural member 11 is exerted on the first columnar structural member 10. A large stress is concentrated on the first columnar structural member 10 near to the fixed end portions 14 of the tabular reinforcing members 12, thereby likely posing a problem of a reduced structural performance. Further, in the case where the tabular reinforcing members 12 are welded to the first columnar structural member 10, the boxing portion at the upper end portion of each tabular reinforcing member 12 may develop a structural defect due to the double effects of the residual welding stress and deterioration of the material of the thermally affected member at the welding fixed end portions, thus posing a problem of a reduced proof stress and a reduced fatigue performance.
FIG. 9 shows another conventional joining structure with U- or V-shaped reinforcing members 13 welded between a first columnar steel structural member 10 and a second structural member 11. In this conventional structure, the joining portion between the first columnar structural member 10 and each reinforcing member 13 has a U- or V-shape along the surface of the first columnar structural member 10. In the case where a large bending moment or axial force is exerted on the first columnar structural member 10, a large stress concentration acting on the first columnar structural member 10 near the U- or V-shaped fixed end portions 15 of the reinforcing members 13 welded to the first columnar structural member 10 may be greatly relaxed. In the case where the U- or V-shaped reinforcing members 13 are welded to the first columnar structural member 10, the residual welding stress as well as the stress concentration at the fixed end portions 15 can be also greatly relaxed.
At the joining portion between the open end 16 of each U- or V-shaped reinforcing member 13 and the second structural member 11, a large stress concentration may occurs on the second structural member 11 in the vicinity of the fixed end portions of the open ends 16 of the U- or V-shaped reinforcing members 13 when the bending moment is exerted on the first columnar structural member 10, thereby likely leading to a problem of a reduced structural performance. Further, in the case where the open end portion 16 of each U- or V-shaped reinforcing member 13 is welded to the second structural member 11, the boxing portion of the open end of the U or V-shaped reinforcing member 13 may develop a structural defect due to the double effects of the residual welding stress and the deterioration of the material of the thermally-affected portion at the fixed end portion, thus posing the problem of a reduced proof stress and fatigue performance.